The innate immune response is the first line of defense in the body's recognition of foreign molecules and, as such, plays an active role in the detection of microbial pathogens. In response, microbial pathogens have evolved intricate means to disarm this response. For example, many Gram-negative bacterial pathogens utilize specialized type 3 secretion systems to deliver tens of bacterial proteins directly into host cells proteins. These proteins, which are referred to as effectors, usurp host cell processes to promote bacterial survival. A common emerging theme is that many effectors suppress the production of pro-inflammatory cytokines by inhibiting steps in signaling pathways that lead to activation of NF-?B, a central innate immune response transcription factor. The majority of the anti-inflammatory effectors characterized to date are found in enteric pathogens, including Salmonella, Shigella, Yersinia and enteropathogenic E. coli species, bacterial, which are constantly interfacing with a variety of cell types in the gastrointestinal tract. Dysregulation ofthe innate immune system is linked to many inflammatory autoimmune-based diseases, including inflammatory bowel disease, psoriasis and rheumatoid arthritis. A major advance in the treatment of these diseases has been the development of therapeutics including TNF inhibitors, humanized antibodies that block activity of this proinflammatory cytokine (i.e., infliximab). However, these agents, like most therapeutic modalities, are delivered systemically, which, in the case of TNF antagonists, results in systemic immunosuppression increasing the incidence of severe infections, including tuberculosis reactivation and brain abscesses, diseases which could be prevented by targeting immunosuppression to sites of disease. Interestingly, although many gram-negative pathogens, particularly those that target the gastrointestinal tract, use specialized secretion systems to deliver proteins directly into host cells, no commensal organism of mammals has yet been identified to encode such a system. The long-term goal of this project is to develop commensal bacteria that are capable of type 3 secretion and to genetically engineer these bacteria to deliver bacterial effector proteins which specifically inhibit NF-?B activation. It is envisioned that these bacteria could be given to patients as a new means to treat inflammatory bowel disease where immunosuppression is limited to the intestines.